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(Circulation. 1961;24:399.)
© 1961 American Heart Association, Inc.

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Muscle Physiology and Contraction Theories

John V. Taggart M.D. RICHARD J. PODOLSKY PH.D.¹

¹ From the Naval Medical Research Institute, National Naval Medical Center, Bethesda, Maryland.

The structural basis of current contraction theories is the double array of thick and thin myofilaments revealed by the electron microscope. The physiologic properties that characterize the contractile process are natural consequences of this structure if (a) during shortening the 2 sets of filaments move relative to each other and (b) the flux of chemical energy through the contractile mechanism is limited by interaction between complementary sites distributed along the 2 sets of filaments. Contraction models fitted to these ideas differ largely in the mechanism by which force is generated. In the sliding model, force is developed by mechanical interaction between the thick and thin filaments, and filament length remains constant during contraction. In the folding model, force is developed in the thin filament, which shortens during contraction. Both models quantitatively account for the force-velocity relation and the Fenn effect. They also accommodate the quick-release phenomenon and predict, at least qualitatively, the isotonic velocity transients that can be seen after quick release from tetanic tension.